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MRI May Be OK for Some Heart Devices

Newer Pacemakers and Defibrillators Offer Possibilities

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Aug. 3, 2004 -- People with heart devices such as pacemakers and defibrillators have long been told to avoid magnetic resonance imaging (MRI) for safety reasons. But a new study shows that MRI may be safe for certain newer devices.

Scientists at Johns Hopkins University in Baltimore spent six months testing devices including nine pacemakers, 18 defibrillators, and 40 electrical systems connecting the device to the heart muscle with the most widely available scanner in the U.S.

The study's focus was to see if MRI interfered with the electrical impulses of the devices. The MRI scanner contains a strong magnet that is believed to cause pacemaker and defibrillator malfunction.

An artificial pacemaker is a small battery-operated device that can help control a regular rhythm to the heart's pumping. An electrical lead is placed on the heart and wires connect the battery-operated device to the heart lead.

A defibrillator is also an electrical device; it gives an electric shock to the heart when it pumps abnormally. By establishing a normal pumping rhythm, the heart can effectively deliver blood to the body organs. Abnormal electrical activity in the heart can lead to sudden death.

The results of the study show most modern devices are safe and perform well in both standard MRI scans and scans using electromagnetic fields at maximum strength.

"You can do a high-energy scan for a long period of time without doing any long-term damage to select devices," says the study's senior author, Henry Halperin, MD, MA, FAHA, professor of medicine, radiology, and biomedical engineering at Johns Hopkins University, in a news release. "These data suggest that certain modern pacemakers and ICDs [implantable cardioverterdefibrillators] may indeed be MRI-safe," write the authors.

Older ICDs, made before 2000, were damaged, but overall, "newer ICD systems and most pacemakers were unaffected," write the researchers. "This may have majorclinical implications for current imaging practices."

But before anyone with a heart device considers getting an MRI, caution should still be exercised. The study's authors write that MRI imaging should be a last resort for patients with heart devices. They suggest MRI scanning be used when all other noninvasive imaging tests don't work.